The present invention relates to a polytrimethylene terephthalate fiber obtained by a melt spinning method and to a method for producing the same. More specifically, the present invention relates to a polytrimethylene terephthalate fiber having a trilobal cross-section suitable for the clothing use and a method for industrially producing such a modified cross-sectional fiber in a stable manner for a long period.
A polyethylene terephthalate (hereinafter referred to as PET) fiber having a modified cross-sectional shape such as a trilobal shape similar to a triangle has already been well-known in the art and is mass-produced on an industrial scale. In general, the modified cross-sectional PET fiber is produced by extruding a polymer either containing no titanium oxide used as a delusterant or containing a relatively small amount thereof in comparison with that in a polymer of a circular cross-section (generally called as a bright polymer) through a spinneret having Y or T-shaped spinning orifices or a modification thereof. The trilobal cross-sectional PET fiber containing a small amount of titanium oxide exhibits a silk-like elegant luster due to the combined effect of the brightness and the cross-sectional shape of the polymer. Accordingly, this fiber has been mass-produced as silky polyester fiber which is evaluated as a high grade product in the clothing field.
Strictly speaking, there are various kinds in the trilobal shape although they commonly have three corners in correspondence to three distal ends of the Y or T-shaped orifice of the spinneret. For instance, there are a group (i) in which an outer periphery of the trilobal cross-section consists of outwardly concave sections except for three corner portions (see FIG. 3); a group (ii) in which an outer periphery of the trilobal-cross-section consists of outwardly convex sections except for three corner portions (see FIG. 1); and a group (iii) in which an outer periphery of the trilobal cross-section is approximately a triangle (see FIG. 2).
On the other hand, the polytrimethylene terephthalate (hereinafter briefly referred to as 3GT) fiber is disclosed in the prior art documents such as (A). Japanese Unexamined Patent Publication No. 52-5320; (B) Japanese Unexamined Patent Publication No. 52-8123; (C) Japanese Unexamined Patent Publication No. 52-8124; (D) Japanese Unexamined Patent Publication No. 58-104216; (E) J. Polymer Science; Polymer Physics Edition vol. 14, pages 263 to 274 (1976); or (F) Chemical Fibers International vol. 45 (April), pages 110 to 111 (1995). According to the description in (F), the 3GT fiber is characterized in a lower Young""s modulus and a higher elastic recovery of elongation (that is, a larger elastic limit) than those of PET fiber due.to its solid structure.
As described above, the PET fiber having a modified cross-sectional shape has been industrially mass-produced and various studies have been made on its cross-sectional shape. Contrarily, there are very few prior arts regarding the 3GT fiber having a modified cross-sectional shape. Japanese Unexamined Patent Publication No. 9-3724 (EP 745711 A1) discloses a 3GT fiber having a modified cross-sectional shape such as a trilobal shape, but this 3GT fiber having a modified cross-sectional shape described in this publication is a BCF fiber for producing a carpet yarn having a single-fiber size of 15 deniers (16.7 dtex) or more and is unsuitable for clothing use. Also, there is nothing but the term xe2x80x9ctrilobalxe2x80x9d regarding the cross-sectional shape thereof, and the details of the shape are not described or suggested.
As described above, the prior art does not describe a 3GT fiber having a trilobal cross-section and a single-fiber size of 8.9 dtex (8 deniers) or less suitable for clothing use as well as the content of titanium oxide necessary for a silky 3GT fiber suitable for clothing use.
In the PET fiber having a modified cross-sectional shape, it has been known that an outer periphery is preferably of a trilobal outwardly concave cross-section to obtain a silky luster. However, the fiber having such a trilobal cross-section exhibits glitter which deteriorates the elegance. Thus, in the modified cross-sectional PET fiber, the trilobal cross-section is insufficient for obtaining the elegant silky luster and, instead, a more complicated multilobal cross-section such as a pentalobal or octalobal cross-section is necessarily adopted (see xe2x80x9cFiber Configurationxe2x80x9d edited by the Fiber Society, pages 170 to 173 (1982)).
On the other hand, in addition to the difference in refractive index between 3GT and PET, a cross-sectional shape of 3GT fiber suitable for obtaining elegant luster and the relationship between the cross-sectional shape and the glossiness have not been known until now.
It is known that when polyester or polyamide is continuously melt-spun for a predetermined period, a contaminant composed of polymer decomposition product or others is adhered to the periphery of spinning orifices of the spinneret (generally called as a white-eye phenomenon or an eye-mucus phenomenon). Since such contaminant disturbs the smooth formation of fiber, fiber breakage increases to interrupt the spinning operation. Therefore, in the industrial sense, the surface of the spinneret is ordinarily wiped off at frequent intervals, to remove the contaminant, for the purpose of maintaining a smooth spinning operation. Since the spinning operation is interrupted by the wiping, the fiber production is disturbed. Accordingly, the interval between the respective wiping operations is preferably as long as possible in view of the operating efficiency and the yield of raw polymer.
A study has been made to prolong the wiping interval by mitigating the white-eye phenomenon. For example, Japanese Unexamined Patent Publication No. 5-78904 proposes the production of polyester fiber having a trilobal cross-section by using a spinning orifice of a modified Y-shaped opening as shown in FIG. 7 in which d/D is in a range from ⅓ to ⅔. In this regard, D is a length (mm) of a vertical line extending from a center of the trilobal orifice to one side of a circumscribed triangle of the outer periphery of the orifice opening, and d is a distance (mm) between the center and a cross point of the above-mentioned vertical line with the arcuate side.
Since the white-eye phenomenon is particularly significant in the case of 3GT fiber, Japanese Unexamined Patent Publication No. 11-200143 proposes to maintain a surface of the spinneret at a certain temperature, to apply a release agent thereto and to determine a polymer surface area per one orifice of the spinneret at a predetermined value for mitigating the white-eye phenomenon. However, there is neither description of how the white-eye phenomenon in a fiber having the modified cross-section occurs nor a suggestion of a countermeasure for mitigating the same.
A first object of the present invention is to provide a 3GT fiber having a uniform trilobal cross-section suitable for clothing, carpets or industrial use, which generates less fluff during the production process and the post-treatment process, and a method for continuously producing this modified cross-sectional fiber for a long period on an industrial scale.
A second object of the present invention is to provide a bright and silky 3GT fiber having a uniform cross-section and a single-fiber size of 8.9 dtex (8 deniers) or less suitable for the clothing use which generates less fluff during the production process and the post-treatment process such as a false-twist texturing process, a weaving or knitting process, and a method for continuously spinning this modified cross-sectional fiber for a long period on an industrial scale.
The inventors of the present invention have diligently studied to achieve the above-mentioned objects and found that there are problems in the production of 3GT fiber as follows:
In comparison with PET, 3GT is liable to generate polymer adhesion or contamination (a so-called white-eye or eye mucus phenomenon) in the vicinity a spinning orifice of a spinneret during the melt-spinning process. Accordingly, in the prior art, fiber breakage occurs in a very short time after starting the spinning, which makes it difficult to continue the spinning operation. Also, when the white-eye phenomenon has occurred, a cross-sectional shape of the resultant fiber having the modified cross-section is liable to vary, or fluff is liable to increase due to the filament breakage. These problems are not solved even though the spinneret having a modified Y-shaped orifice shown in FIG. 7 is used.
Also, the 3GT fiber exhibits a unique frictional characteristic in comparison with PET fiber, and has high coefficients of static and dynamic friction between fiber/fiber, fiber/metal, and fiber/ceramics. Thereby, the fiber breakage and fluff are liable to occur due to the friction during the drawing or post-treatment process. Particularly, this tendency is particularly true in a so-called bright polymer containing less of the titanium oxide used as a delusterant.
Further, the inventors of the present invention have found, as a result of diligent study, that it is possible to suppress the contamination of a spinning orifice with polymer (the white-eye or eye mucus phenomenon) and to prolong the wiping interval to as long as twelve hours or more by using a spinneret of a special configuration, more concretely closer to a triangle rather than a Y-shape, and limiting the spinning temperature, the surface temperature of the spinneret and the linear speed V of the extruded polymer to a specified range.
Also, it has been found that the fiber of the modified cross-section obtained from the inventive method has a uniform cross-sectional shape and the generation of fluff is less during treatment. Particularly, it has been found that if the content of titanium oxide in 3GT polymer is limited to the specified range, the frictional characteristic becomes proper when the 3GT polymer is used as a bright polymer, whereby the generation of fiber breakage or fluff is suppressed during the drawing and post-treatment process of the fiber having a trilobal cross-section. Simultaneously therewith, a silky luster is exhibited.
That is, the present invention is:
1. A 3GT fiber having a modified cross-section, composed of polytrimethylene terephthalate comprising 95 mol % or more of trimethylene terephthalate repeating units and 5 mol % or less of other ester repeating units, and having an intrinsic viscosity [xcex7] in a range from 0.7 to 1.3 (dl/g), wherein the fiber has a trilobal cross-section in which the outer periphery consists solely of outwardly convex sections or both of outwardly convex sections and straight sections.
2. A 3GT fiber having a modified cross-section as defined by claim 1, wherein the fiber contains titanium oxide in a range from 0.03 to 0.15 wt %, and has a fiber size of 8.9 dtex (8 deniers) or less.
3. A 3GT fiber having a modified cross-section as defined by claim 1 or 2, wherein the modification degree is in a range from 1.15 to 1.35.
4. A 3GT fiber having a modified cross-section as defined by claim 1, 2 or 3, wherein the glossiness is in a range from 50 to 75.
5. A method for producing a 3GT fiber having a modified cross-section, comprising a step of extruding polytrimethylene terephthalate comprising 95 mol % or more of trimethylene terephthalate repeating units.and 5 mol % or less of other ester repeating units, and having an intrinsic viscosity [xcex7] in a range from 0.7 to 1.3 (dl/g), through a spinneret having spinning orifices of a trilobal opening, wherein.
i) the outer periphery of the trilobal cross-section comprises three semicircular corners and outwardly concave arcuate sections connecting every adjacent corner with the others, and all of the d/D values for three sides are in a range from 0.70 to 1.0 (wherein D is a length (mm) of a vertical line extending from a center of the trilobal orifice to one side of a circumscribed triangle in the outer periphery of the orifice opening, and d is a distance (mm) between the center and a cross point of the above-mentioned vertical line with the arcuate side);
ii) a spinning temperature is in a range from 255 to 275xc2x0 C.;
iii) a surface temperature of the spinneret is in a range from 250 to 275xc2x0 C.; and
iv) a product of a linear speed V of the melted polymer extruded from the spinneret and the intrinsic viscosity [xcex7] of 3GT; i.e., Vxc3x97[xcex7] is in a range from 4 to 13 (m/min) (dl/g).
6. A method for producing a 3GT fiber having a modified cross-section as defined by claim 5, wherein the 3GT contains titanium oxide in a range from 0.03 to 0.15 wt %.
7. A 3GT fiber having a modified cross-section obtained by a method defined by claim 5 or 6.